1. Field of the Invention
The present invention is in the field of chemical processing of irradiated nuclear fuel to extract the radioactive medical isotope molybdenum-99 (Mo-99), and in particular, relates to the extraction of Mo-99 from the fuel of a homogeneous solution nuclear reactor using an inorganic sorbent.
2. Description of the Prior Art
At the present time more than 50% of the world""s annual production of radionuclides are used for medical purposes, such as for the early diagnoses of diseases and for therapy. A basic condition of the use of radionuclides in medicine is the requirement that the radiation exposure of a patient be minimal. This necessitates the use of short-lived radionuclides. A nuclide with a short half-life, however, creates difficulties in transportation and storage. The most used radionuclide for medical purposes is Mo-99 with a half-life of 66 hours. Mo-99 decay results in Tc-99 m with a half-life of 6 hours and about 140 keV of gamma (xcex3) energy convenient for detection. Currently, more than 70% of diagnostic examinations are performed using this radionuclide.
A number of techniques exist for the recovery of Mo-99 from various material xe2x80x9ctargetsxe2x80x9d irradiated in a nuclear reactor. Once the irradiated targets are removed from the reactor, organic agents are used to extract the Mo-99. Extraction must take place in a low radiation environment because organic extraction agents and organic ion-exchange resins have poor radiation resistance.
U.S. Pat. No. 5,910,971 describes a method and apparatus for the generation of Molybdenum-99 in the uranyl sulfate nuclear fuel of a homogeneous solution nuclear reactor. The nuclear fuel containing Molybdenum-99 is pumped through an organic sorbent for extraction of the Molybdenum-99 in a closed cycle system. U.S. Pat. No. 5,962,597, describes a particular organic sorbent for the extraction of Mo-99 from a solution nuclear reactor such as that found in the ""971 patent.
The present invention details an inorganic sorbent that efficiently and selectively extracts Mo-99 from highly radioactive solutions of uranium. This sorbent has high radiation resistance permitting its use in the high radiation zone of a reactor. This facilitates a closed cycle extraction process that maintains the uranium concentration of the nuclear fuel through many Mo-99 extraction cycles while minimizing radioactive waste disposal problems. It also can potentially lower the operating costs due to the multiple reuse of the sorbent.
Mo-99 is extracted from a uranyl sulfate nuclear-fueled homogeneous-solution nuclear reactor under recirculation conditions. The reactor solution containing Molybdenum-99 is pumped through a loose layer of an inorganic sorbent that sorbs the Molybdenum-99. The inorganic sorbent is a composition of hydrated titanium dioxide containing 5 to 40 mole percent of zirconium hydroxide. It is in the form of pellets, preferably 0.1 to 2.0 mm in size, having a specific surface area of 100 to 350 m2/g. The sorbent has high radiation, chemical, and mechanical resistance properties, thus allowing the sorption process to take place in the high radiation zone of the reactor.